Imageable polymers

ABSTRACT

The present invention relates to hydrogels comprising 1,2-diol or 1,3-diol groups acetalised with a radiopaque species of one or more covalently bound radiopaque halogens which are imageable during embolization therapy. The invention further relates to methods of making radiopaque polymers and radiopaque hydrogel microspheres to provide an imageable drug delivery system.

This invention relates to radiopaque polymers and to methods for makingthem. The invention provides radiopaque hydrogels and, in particular,radiopaque hydrogel microspheres, which are imageable duringembolization procedures. The microspheres can be loaded with drugs orother therapeutic agents to provide an imageable drug delivery system.

Radiopacity, refers to the property of obstructing, or attenuating, thepassage of electromagnetic radiation, particularly x-rays. Radiopaquematerials are therefore visible in X-ray radiographs or during X-rayimaging and under fluoroscopy. Radiopaque materials consequently findmany uses in radiology and medical imaging techniques such as computedtomography (CT) and fluoroscopy.

Embolization of blood vessels (blocking the blood flow) is an importantmedical procedure in the treatment of tumours, fibroids and vascularmalformations, in which an embolus, or blockage is introduced into ablood vessel to reduce blood flow and induce atrophy of tumours andmalformations. There is a range of embolic materials in clinical usethat require transcatheter delivery to the site of embolization.Recently the use of microspheres (also referred to herein as “beads”) asinjectable embolic materials has become popular because their shape andsize can be controlled making them more predictable in use than previousparticulate material.

Imaging of embolization procedures is important because it provides theclinician with the ability to monitor the precise location of theembolic material and ensure that it is administered to, and remains in,the correct position in the vasculature, thus improving proceduraloutcomes and reducing procedural risk. Imaging is currently onlypossible when using inherently radiopaque embolic materials or by mixingnon-radiopaque embolic particles with radiopaque materials.

Iodinated polyvinyl alcohol (I-PVA) is a radiopaque embolic material inthe form of a viscous liquid which precipitates in aqueous conditionsencountered in vivo. However, the precise location at which the embolusis formed can be inconsistent risking precipitation occurring in an offtarget location.

Contrast agents, such as Ethiodol® and Isovue® are, however, routinelymixed with embolic particles to impart radiopacity to an injectablecomposition. Although such compositions are useful, the differentphysical properties of the aqueous suspension of embolic particle andthe contrast agent results in different in-vivo localisation. Afteradministration, it is the contrast agent which is visible rather thanthe embolic particle, and the contrast agent and the embolic particlemay not reside at the same location in tissue.

There is a need, therefore, to combine the predictability andreproducibility benefits of embolic microspheres with the radiopacity ofcontrast agents.

EP1810698 describes a process for forming stable radiopaque embolicbeads (also referred to herein as RO beads or RO microspheres) in whichPVA hydrogel embolic beads are loaded with iodinated oils to make themradiopaque. The mechanism by which the oil is held within the bead isunclear. Furthermore, since the oil is a mixture of ethiodised fattyacids, the end product is not closely defined and this approach does notprovide control over elution of the contrast agent from the bead nordoes it contemplate the impact of contrast agent on the loading andelution of drug.

WO2011/110589 describes synthesis of an iodinated poly(vinyl alcohol) bygrafting iodobenzoyl chloride to poly(vinyl alcohol) via ester linkages.Whilst this polymer is demonstrated to be radiopaque, the processresults in a water insoluble polymer, which cannot then be formed intomicrospheres through the water-in-oil polymersation processes normallyused to generate hydrogel microspheres with desirable embolizationproperties. The same publication mentions microspheres but contains nodisclosure as to how this is achieved.

Mawad et al (Biomacromolecules 2008, 9, 263-268) describes chemicalmodification of PVA-based degradable hydrogels in which covalently boundiodine is introduced into the polymer backbone to render the polymerradiopaque. Iodine is introduced by reacting 0.5% of the pendent alcoholgroups on PVA with 4-iodobenzoylchloride. The resulting polymer isbiodegradable, embolizes via precipitation and is not formed intomicrospheres.

There is clearly a need, therefore, for radiopaque embolic materialswhich combine the embolization efficiency and reproducibility of embolicbeads with the radiopacity of contrast agents, such as ethiodized oils,in a single product. The ideal embolic particle is one which isintrinsically radiopaque and which is stable and reproducible, in sizeand physical properties such that the clinician can perform and imagethe embolization procedure with more certainty that visible contrastresults from the embolic particle. The injection and deposition of thesebeads into the vascular site could be monitored but monitoring duringclinical follow up would also be possible to monitor the effects ofembolization, ensure embolic remains in the desired location and toidentify regions at risk for further treatment. The time window in whichfollow-up imaging can be obtained is increased significantly overexisting methods.

Radiopacity (the ability to attenuate X-rays) can be quantifiedaccording to the Hounsfield scale. Hounsfield units measure radiopacityon a volume (voxel) basis. A typical voxel in X-ray computed tomography(CT) is approximately 1 mm³ and so individual microspheres of a diameterof the order of 100 um must have a high radiopacity in order that it, ora collection of them in a vessel (for example) will increase theradiopacity of that voxel and so be visualised. Radiopacity of greaterthan 100 HU and preferably greater than 500 HU would be appropriate.

In addition to good radiopacity, the ideal embolic bead would haveproperties which enable efficient drug loading and elution such thatchemoembolization procedures may be monitored with confidence.

The applicants have established that by utilizing relativelystraightforward chemistry, it is possible modify polymers to make themradiopaque. A low molecular weight aldehyde comprising one or morecovalently attached radiopaque halogens (such as bromine or iodine) iscoupled to the polymer by reaction with 1,3 diol groups of the polymer.Reaction with 1,2 glycols is also possible. This forms a cyclic acetal(a dioxane ring in the case of reaction with 1,3,diols) to which iscovalently coupled, a halogenated group. The halogenated group has amolecular weight of less than 1000 Daltons and is typically less than750 Daltons. Typically the minimum is 156 daltons.

The halogenated group typically has between 6 and 18 carbons, butpreferably between 6 and 10; and optionally one oxygen atom; andcomprises an aromatic ring comprising one or more covalently attachedradiopaque halogens. The aromatic ring is preferably a phenyl group.

The chemistry results in a polymer having a defined radiopaque groupcovalently attached to the polymer, in a predictable and controllablefashion. It may be performed on any diol-containing polymer and it isparticularly suited to hydrogel polymers and pre-formed microspheres,such that non-radiopaque microspheres may be rendered intrinsically andpermanently radiopaque, without adversely affecting the physicalproperties of the microsphere (i.e. size, spherical shape, high watercontent, swellability, and compressibility). The radiopaque microsphereshave similar, and/or better, drug loading capacities and/or elutionproperties to the non-radiopaque beads from which they are formed. Theradiopacity of the microsphere is permanent or sufficiently long-livedto allow for monitoring during clinical follow up.

The ability to post-process pre-formed beads provides a degree offlexibility in terms of manufacturing in that the same manufacturingprocess can be used for radiopaque and non-radiopaque beads and sizeselection or sieving can be made either prior to post-processing so thatonly a particular size or size range of beads may be made radiopaque, orif necessary, after post processing, so that sizing takes into accountany variation in bead size due to the radiopacifying process.

Accordingly, in a first aspect, the present invention provides a polymercomprising 1,2-diol or 1,3-diol groups acetalised with a radiopaquespecies. Acetalisation with a radiopaque species results in theradiopaque species being coupled to the polymer through a cyclic acetalgroup (a dioxane in the case of 1,3 diol polymers). The radiopacity ofthe polymer is thus derived from having a radiopaque material covalentlyincorporated into the polymer via cyclic acetal linkages.

As used herein, “radiopaque species” and “radiopaque material” refers toa chemical entity, or a substance modified by such a chemical entity,which is visible in X-ray radiographs and which can be resolved, usingroutine techniques, such as computed tomography, from the medium thatsurrounds the radiopaque material or species.

The term microsphere or bead refers to micron sized spherical or nearspherical embolic materials. The term particle or microparticle refersto embolic particles that are irregular in shape and are generallyderived e.g. from breaking up a larger monolith.

Where the text refers to “halogen” or “halogenated” iodine is preferred,unless otherwise stated.

Reference to the level of radiopacity in HU refers to measurementscarried out by X-Ray Micro Computer Tomography, and preferably whenmeasured using a 0.5 mm aluminium filter and a source voltage of 65 kV,preferably in an agarose phantom as described herein (Example 12),preferably using the instrument and conditions described herein (Example12). Reference to radiopacity in terms of greyscale units also refers tomeasurements carried out by X-Ray Micro Computer Tomography under theseconditions.

Reference to “wet beads” or “fully hydrated beads” means beads fullyhydrated in normal saline (0.9% NaCl 1 mM phoshate buffer pH7.2 to 7.4)as packed volume (e.g. as quantified in a measuring cylinder).

In this aspect and others, the polymer can be any one which comprises1,2-diol or 1,3 diol groups or a mixture thereof. Preferably the polymercomprises a high degree of the diol groups throughout the polymerbackbone, such as a polyhydroxypolymer. The polymer is suitably ahydrogel or other cross-linked polymer network. Particularly suitablepolymers are those which comprise polyvinyl alcohol (PVA) or copolymersof PVA. PVA based hydrogels are particularly preferred as these are wellknown in the art and are used extensively in embolization procedures.

In a particular embodiment, the polymer comprises a PVA backbone whichhas pendant chains bearing crosslinkable groups, which are crosslinkedto form a hydrogel. The PVA backbone has at least two pendant chainscontaining groups that can be crosslinked, such as acetates andacrylates. The crosslinkers are desirably present in an amount of fromapproximately 0.01 to 10 milliequivalents of crosslinker per gram ofbackbone (meq/g), more desirably about 0.05 to 1.5 meq/g. The PVApolymers can contain more than one type of crosslinkable group. Thependant chains are conveniently attached via the hydroxyl groups of thepolymer backbone are attached via cyclic acetal linkages to the 1,3-diolhydroxyl groups of the PVA

Cross linking of the modified PVA may be via any of a number of means,such as physical crosslinking or chemical crosslinking. Physical crosslinking includes, but is not limited to, complexation, hydrogen bonding,desolvation, Van der wals interactions, and ionic bonding. Chemicalcrosslinking can be accomplished by a number of means including, but notlimited to, chain reaction (addition) polymerization, step reaction(condensation) polymerization and other methods as will be routine forthe polymer chemist.

Crosslinked groups on the PVA polymer backbone are suitablyethylenically unsaturated functional groups, such as acetates, which canbe crosslinked via free radical initiated polymerization withoutrequiring the addition of an aldehyde crosslinking agent. Preferably,the PVA polymer comprises pendent actetate groups formed from theacetalisation of PVA with N-acryloyl-aminoacetaldehyde dimethylacetal(NAADA). Such a modification of PVA is described in U.S. Pat. No.5,583,163. An example of this type of modified PVA is Nelfilcon A.

The cross-linkable PVA is suitably cross-linked with an additionalvinylic comonomer and, suitably a hydrophilic vinylic comonomer such ashydroxy-substituted lower alkyl acrylates and methacrylates, acrylamidesand methacrylamides. In a particular embodiment the modified PVA asdescribed above is crosslinked with 2-acrylamido-2-methylpropanesulfonicacid (AMPS® monomer from Lubrizol Corporation) to provide an acrylamidopolyvinyl alcohol-co-acrylamido-2-methylpropane sulfonate hydrogel. In apreferred embodiment the cross-linking reaction is performed as aninverse emulsion polymerisation reaction to yield the acrylamidopolyvinyl alcohol-co-acrylamido-2-methylpropane sulfonate hydrogel inthe form of microspheres.

The polymer or hydrogel of the invention is radiopaque by virtue of acovalently attached radiopaque material throughout the polymer in theform of a cyclic acetal. Reactions for the formation of cyclic acetalsare well known in organic chemistry and, thus, any radiopaque specieswhich is able to form cyclic acetals is envisaged within the scope ofthe invention. Many materials are known to be radiopaque, such asIodine, Bismuth, Tantalum, Gadolinium, Gold, Barium and Iron. Electrondense elements, such as the halogens, are particularly useful. Bromine,chlorine, fluorine and iodine can readily be incorporated into organicmolecules which are able to form cyclic acetal linkages and provide ahigh degree of radiopacity. Consequently, in a particular embodiment theradiopaque polymer comprises a covalently attached halogen, preferablyiodine. The radiopaque halogen is covalently attached to an aromaticgroup to form the radiopaque species which is linked to the polymerthrough the cyclic acetal. The aromatic group may comprise 1, 2, 3 or 4covalently attached radiopaque halogens such as bromine or iodine. Thegroup preferably comprises a phenyl group to which is covalentlyattached 1, 2, 3 or 4 such radiopaque halogens. Thus the polymerconveniently comprises a halogenated group (X in the formula below),comprising covalently bound radiopaque halogens, such as iodine, whichare attached to the polymer via a cyclic acetal.

Acetalisation with a radiopaque species results in the radiopaquespecies being coupled to the polymer through a cyclic acetal group asillustrated below. The radiopaque polymer has or comprises a structureaccording to General Formulas I (in PVA J is —CH₂—) or II (whichillustrates other polymers with 1,2 or 1,3 diols): Control of the numberof such groups acetalised (n) in the polymers controls the amount ofiodine present and therefore the radiopacity. The number of diols per gmof material is discussed below.

Wherein X is a group substituted by one or more halogens and preferablyone or more bromine or iodine moieties and n is at least one.

J is a group —CH₂— or is a bond.

X is preferably a group of the formula

wherein Z is a linking group bonded to the cyclic acetal, or is absent,such that the phenyl group is bonded to the cyclic acetal;

if Z is present, then Z is C₁₋₆ alkylene, C₁₋₆ alkoxylene or C₁₋₆alkoxyalkylene;

Hal is 1, 2, 3 or 4 covalently attached radiopaque halogens

Preferably if Z is present, Z is a methylene or ethylene group or is agroup —(CH₂)_(p)—O—(CH₂)_(q)— wherein q is 0, 1 or 2 and p is 1 or 2;more preferably a group selected from —CH₂O—, —CH₂OCH₂— and —(CH₂)₂O—,

In particular Z is —CH₂OCH₂— or —CH₂O— or is absent

Hal is in particular 3 or 4 Bromines of iodines and preferably iodines,such as 2,3,5 or 2,4,6 triiodo or 2,3,4,6 tetraiodo

J is preferably —CH₂—.

Thus preferably, radiopaque iodine is incorporated into the polymer inthe form of an iodinated phenyl group. As above, the iodinated phenylgroups are incorporated into the polymer through cyclic acetal linkages.

Groups, such as those described above and in particular halogenated(e.g. iodinated) phenyl groups, are useful because they can be mono, di,tri or even tetra-substituted in order to control the amount of thehalogen, such as iodine, that is incorporated into the radiopaquepolymer, and hence control the level of radiopacity.

The potential level of halogenation is also influenced by the level of1,3 or 1,2 diol groups in the polymer starting material. The level canbe estimated based on the structure of the polymer and the presence orother wise of any substitutions of the —OH groups, for example by crosslinkers or other pendent groups. Polymers having a level of —OH groupsof at least 0.1 mmol/g of dried polymer are preferred. Polymers having alevel of at least 1 mmol/g are more preferred. An excellent level ofradiopacity has been achieved with polymers having greater than 5 mmol/g—OH groups, (2.5 mmol/g diols).

It will be understood by the person skilled in the art that the amountof iodine, or other radiopaque halogen, in the polymer may also becontrolled by controlling the degree of acetalisation in the polymer. Inthe present invention, the polymer comprises up to 50% of acetaliseddiol groups. Preferably at least 10% of the diol groups in the polymerare acetalised and more preferably at least 20% of the diols groups areacetalised. Whether the amount of halogen (e.g. iodine) in the polymeris controlled by increasing the substitution, for example on a phenylring, or by controlling the degree of acetalisation of the polymer, theresulting polymer contains at least 10% halogen by dry weight (weight ofhalogen/total weight). Preferably the polymer contains at least 20%halogen by dry weight and preferably greater than 30%, 40%, 50% or 60%halogen by dry weight. A useful contrast is obtained with polymershaving between 30 and 50% halogen by dry weight.

Halogen content may also be expressed as amount of halogen (in mg) perml of beads. This refers to the amount of halogen per ml of fullyhydrated beads in saline as a packed volume (e.g., as quantified in ameasuring cylinder). The present invention provides beads with levels ofhalogen (particularly iodine) of, for example, greater than 15 mg per mlof wet beads. Halogen (particularly iodine) content of greater than 25or 50 mg preferably greater than 100 mg per ml of beads have providedgood results.

The present invention is particularly suited to hydrogels and, inparticular, hydrogels in the form of microparticles or microspheres.Microspheres are particularly useful for embolization as sizes ofmicrosphere can be controlled, for example by sieving) and unwantedaggregation of embolic avoided due to the spherical shape. Microspherescan be made by a number of techniques known to those skilled in the art,such as single and double emulsion, suspension polymerization, solventevaporation, spray drying, and solvent extraction.

Microspheres comprising poly vinylalcohol or vinyl alcohol copolymersare described, for example in Thanoo et al Journal of AppliedBiomaterials, Vol. 2, 67-72 (1991); WO0168720, WO03084582; WO06119968and WO04071495, (which are incorporated herein by reference). In aparticular embodiment the hydrogel microspheres are prepared from PVAmodified with N-acryloyl-aminoacetaldehyde dimethylacetal (NAADA), asdescribed above (and disclosed in U.S. Pat. No. 5,583,163) andcross-linked with 2-acrylamido-2-methylpropanesulfonic acid, asdescribed above. Hydrogel microspheres of this type are described inU.S. Pat. No. 6,676,971 and U.S. Pat. No. 7,070,809.

Microspheres can be made in sizes ranging from about 10 μm (microns) to2000 μm. Smaller sizes may pass through the microvasculature and lodgeelsewhere. In most applications it will be desirable to have a smallsize range of microspheres in order to reduce clumping and providepredictable embolisation. The process used to make the microspheres canbe controlled to achieve a particular desired size range ofmicrospheres. Other methods, such as sieving, can be used to even moretightly control the size range of the microspheres.

In a particular embodiment hydrogel or non hydrogel microspheresaccording to the invention have a mean diameter size range of from 10 to2000 μm, more preferably 20 to 1500 μm and even more preferably, 40 to900 μm. Preparations of microspheres typically provide particles in sizeranges to suit the planned treatment, for example 100-300, 300-500,500-700 or 700-900 microns. Smaller particles tend to pass deeper intothe vascular bed and so for certain procedures, particles in the range40-75, 40-90 and 70-150 microns are particularly useful.

In a particular embodiment, the polymer is a hydrogel microsphere with anet negative charge at physiological pH (7.4).

Radiopacity can be quantified according to the Hounsfield scale, onwhich distilled water has a value of 0 Hounsfield units (HU), and airhas a value of −1000 HU. Conveniently the embolic microsphere will haveradiopacity greater than 100 HU and even more preferably greater than500 HU. Using the approach described herein, it has been possible toprepare radiopaque microspheres with a radiopacity of greater than 10000HU. Preferred microspheres have a radiopacity greater than 2000, 3000,4000 or 5000 HU. Radiopacity of these levels allows the microspheres tobe differentiated from blood (30-45 HU), liver (40-60 HU) brain (20-45HU) and soft tissue (100-300 HU), for example.

Radiopacity can also be expressed in Grey Scale units, between 0 and 255after background subtraction, according to American Society for Testingand Materials (ASTM) F-640.

A further aspect of the invention therefore provides, a radiopaquemicrosphere as described herein, in the first aspect, having aradiopacity of at least 500 HU.

The hydrogel microspheres of this embodiment may be used in compositionswith suitable excipients or diluents, such as water for injection, andused directly to embolise a blood vessel. Thus a further aspect of theinvention provides a pharmaceutical composition comprising a hydrogelmicrosphere as described herein and a pharmaceutically acceptablecarrier or diluent.

Consequently pharmaceutical compositions comprising radiopaque hydrogelmicrospheres which are formed from a polymer comprising 1,2-diol or1,3-diol groups acetalised with a radiopaque species as describedherein, form a further aspect of the invention. It is preferred that thepolymer comprises an iodinated aromatic group covalently bound to thepolymer through cyclic acetal linkages as described above.

Pharmaceutical compositions comprising the radiopaque microspheres mayalso comprise additional radiopaque materials, such as, for examplecontrast agents, (either ionic or non ionic, including oily contrastagents such as ethiodised poppy seed oil (Lipiodol®). Suitable non ioniccontrast agents include iopamidol, iodixanol, iohexol, iopromide,iobtiridol, iomeprol, iopentol, iopamiron, ioxilan, iotrolan, iotrol andioversol.

Ionic contrast agents may also be used, but are not preferred incombination with drug loaded ion exchange microspheres since high ionicconcentrations favour disassociation of the ionic drugs from the matrix.Ionic contrast agents include diatrizoate, metrizoate and ioxaglate.

The microspheres may be dried by any process that is recognised in theart, however, drying under vacuum, such as by freeze drying(lyophilisation) is advantageous as it allows the microspheres to bestored dry and under reduced pressure. This approach leads to improvedrehydration as discussed in WO07147902 (which is incorporated herein byreference). Typically, the pressure under which the dried microspheresare stored is less than 1 mBar (guage).

Alternatively, or additionally, an effective amount of one or morebiologically active agents can be included in the embolic compositionsIt may be desirable to deliver the active agent from the formedradiopaque hydrogel or from microspheres. Biologically active agentsthat it may be desirable to deliver include prophylactic, therapeutic,and diagnostic agents including organic and inorganic molecules andcells (collectively referred to herein as an “active agent”,“therapeutic agent” or “drug”). A wide variety of active agents can beincorporated into the radiopaque hydrogels and microspheres. Release ofthe incorporated active agent from the hydrogel is achieved by diffusionof the agent from the hydrogel in contact with aqueous media, such asbody fluids, degradation of the hydrogel, and/or degradation of achemical link coupling the agent to the polymer. In this context, an“effective amount” refers to the amount of active agent required toobtain the desired effect.

Accordingly in a further aspect the invention provides a pharmaceuticalcomposition comprising a radiopaque hydrogel microsphere as describedabove and a therapeutic agent wherein the therapeutic agent is absorbedinto the hydrogel matrix. A further aspect of the invention provides acomposition comprising one or more radiopaque hydrogel microspheres asdescribed herein, the microspheres additionally comprising one or moretherapeutic agents, such as pharmaceutical actives. Examples of activeagents, or pharmaceutical actives that can be incorporated include, butare not limited to, anti-angiogenic agents, cytotoxics andchemotherapeutic agents, making the microspheres particularly useful forchemoembolization procedures.

In a particularly advantageous embodiment, the radiopaque hydrogelmicrospheres of the invention have a net charge such that charged drugsmay be loaded into the microsphere e.g. by an ion exchange mechanism. Asa result, the therapeutic agent is electrostatically held in thehydrogel and elutes from the hydrogel in electrolytic media, such asphysiological saline, or in-vivo, e.g. in the blood or tissues, toprovide a sustained release of drug over several hours, days or evenweeks. In this embodiment it is particularly useful if the radiopaquehydrogel microspheres of the invention have a net negative charge over arange of pH, including physiological conditions (7.4) such thatpositively charged drugs may be controllably and reproducibly loadedinto the microsphere, and retained therein electrostatically, forsubsequent prolonged elution from the hydrogel in-vivo. Such charges maybe derived from ion exchange groups such as carboxyl or sulphonategroups attached to the polymer matrix. It will be understood that drugswithout charge at physiological pHs may still be loaded intomicrospheres of the invention and this may be particularly advantageouswhen rapid elution or a “burst effect” is desired, for example,immediately after embolization or simply for rapid drug delivery totissue in cases where embolization is not required or necessary, orwhere their low solubility under physiological conditions determinestheir release profile rather than ionic interaction.

Particularly preferred examples of drugs which may be loaded in this wayinclude, but are not limited to, camptothecins (such as irinotecan andtopotecan) and anthracyclines (such as doxorubicin, daunorubicin,idarubicin and epirubicin), antiangiogenic agents (such as vascularendothelial growth factor receptor (VEGFR) inhibitors, such as axitinib,bortezomib, bosutinib canertinib, dovitinib, dasatinib, erlotinibgefitinib, imatinib, lapatinib, lestaurtinib, masutinib, mubitinib,pazopanib, pazopanib semaxanib, sorafenib, tandutinib, vandetanib,vatalanib and vismodegib.), microtubule assembly inhibitors (such asvinblastine, vinorelbine and vincristine), Aromatase inhibitors (such asanastrazole), platinum drugs, (such as cisplatin, oxaliplatin,carboplatin and miriplatin), nucleoside analogues (such as 5-FU,cytarabine, fludarabine and gemcitabine) and. Other preferred drugsinclude paclitaxel, docetaxel, mitomycin, mitoxantrone, bleomycin,pingyangmycin, abiraterone, amifostine, buserelin, degarelix, folinicacid, goserelin, lanreotide, lenalidomide, letrozole, leuprorelin,octreotide, tamoxifen, triptorelin, bendamustine, chlorambucil,dacarbazine, melphalan, procarbazine, temozolomide, rapamycin (andanalogues, such as zotarolimus, everolimus, umirolimus and sirolimus)methotrexate, pemetrexed and raltitrexed.

The radiopaque hydrogel microspheres are preferably water-swellable butwater-insoluble.

In an embodiment the beads are water-swellable but have some solubilityin water. In this embodiment, the extent of swelling may be controlledby the use of aqueous salt solutions or suitable solvents, as may bedetermined by routine experimentation. This may be particularlyapplicable to PVA polymers which are non-covalently cross-linked.

In another embodiment the beads are water and solvent-swellable but arealso biodegradable. In this embodiment the beads biodegrade in-vivo overa period ranging from 4 weeks to 24 months. Biodegradable polymerscomprising PVA are disclosed in, for example, WO2004/071495, WO2012/101455 and Frauke-Pistel et al. J. Control Release 2001 May 18;73(1):7-20.

As discussed above the radiopaque polymers of the invention may be madeby utilizing straightforward chemistry to directly modify pre-formedmicrospheres to make them intrinsically radiopaque. Accordingly, in afurther aspect, the invention provides a method of making a radiopaquepolymer comprising reacting a polymer comprising 1,2-diol or 1,3-diolgroups with a radiopaque species capable of forming a cyclic acetal withsaid 1,2-diol or 1,3 diols preferably under acidic conditions.

Particularly the radiopaque species capable of forming the cyclic acetalcomprises a covalently bound radiopaque halogen such as iodine asdescribed herein. Particularly the halogen is covalently bound to anaromatic group such as a phenyl group.

The chemistry is particularly suited to polymers with a backbone ofunits having a 1,2-diol or 1,3-diol structure, such as polyhydroxypolymers. For example, polyvinyl alcohol (PVA) or copolymers of vinylalcohol containing a 1,3-diol skeleton. The backbone can also containhydroxyl groups in the form of 1,2-glycols, such as copolymer units of1,2-dihydroxyethylene. These can be obtained, for example, by alkalinehydrolysis of vinyl acetate-vinylene carbonate copolymers.

Other polymeric diols can be used, such as saccharides. In a particularembodiment, the polymer is cross-linked, such as cross-linked PVA orcopolymers of PVA.

Polyvinyl alcohols, that can be derivatized as described hereinpreferably have molecular weight of at least about 2,000. As an upperlimit, the PVA may have a molecular weight of up to 1,000,000.Preferably, the PVA has a molecular weight of up to 300,000, especiallyup to approximately 130,000, and especially preferably up toapproximately 60,000.

In a preferred embodiment, the PVA is a cross-linked PVA hydrogel, inwhich PVA modified with N-acryloyl-aminoacetaldehyde dimethylacetal(NAADA) is cross-linked with 2-acrylamido-2-methylpropanesulfonic acid,as described above, preferably in the form of microspheres, as describedin U.S. Pat. No. 6,676,971 and U.S. Pat. No. 7,070,809.

The radiopaque species is acetalised, and covalently attached to thepolymer, through diol groups. Preferred radiopaque species are electrondense chemical moieties, such as simple organic molecules ororganometallic complexes providing radiopacity greater than +1 HU, andwhich comprises a reactive moiety that enables formation of a cylicacetal with diol groups on the polymer. Particular reactive moietiesinclude aldehydes, acetals, hemiacetals thioacetals and dithioacetals

In a particular embodiment the radiopaque species comprises bromine oriodine. This is convenient because small organic molecules in whichbromine or iodine has been substituted are commercially available or maybe prepared using chemistry well known in the art. For example,iodinated or brominated aldehydes are radiopaque and are readilyincorporated into diol-containing polymers using the method of theinvention. Particularly useful radiopaque species include iodinated orbrominated benzyl aldehydes, iodinated phenyl aldehydes and iodinatedphenoxyaldehydes.

The reaction of radiopaque aldehydes with diol-containing polymers workssurprisingly well with hydrogel polymers, which have been pre-formed,for example into microspheres (although other preformed hydrogelstructures such as coatings are contemplated). Thus, in another aspectthe invention provides a method of making a radiopaque hydrogelmicrosphere comprising the steps of:

(a) swelling a pre-formed hydrogel microsphere comprising a polymer with1,2-diol or 1,3-diol groups in a solvent capable of swelling saidmicrosphere; and (b) mixing or contacting the swollen microspheres witha solution of a radiopaque species capable of forming a cyclic acetalwith said 1,2 or 1,3 diols under acidic conditions; and (c) extractingor isolating the microspheres.

The extracted or isolated microspheres may then be used directly,formulated into pharmaceutical compositions as described above or driedfor long-term storage.

In a preferred embodiment, the reaction is performed on an acrylamidopolyvinyl alcohol-co-acrylamido-2-methylpropane sulfonate hydrogelmicrosphere. Examples of such microspheres are described in U.S. Pat.No. 6,676,971 and U.S. Pat. No. 7,070,809.

The reaction is conveniently conducted in polar organic solvent, andmore particularly, polar aprotic solvents such as tetrahydrofuran (THF),ethyl acetate, acetone, dimethylformamide (DMF), acetonitrile (MeCN) anddimethyl sulfoxide (DMSO), although suitable solvents will determined bythe skilled person through routine experimentation and/or considerationof solvent properties such as boiling point, density etc.

The reaction is rapid and may be conducted at room temperature or atelevated temperature to improve yields and decrease reaction time. In apreferred embodiment the reaction is conducted at a temperature greaterthan 25° C. and suitably greater than 40° C. but less than 135° C. andpreferably less than 80° C. Reaction temperatures between 50 and 75° C.are particularly useful. At elevated temperatures the conversion ofhydrogel bead to radiopaque hydrogel bead can be accomplished in aslittle as 2-3 hours.

As above, the radiopaque species comprises a functional group selectedfrom the group consisting of aldehydes, acetals, hemiacetals,thioacetals and dithioacetals, and comprises iodine or other radiopaquehalogen. In this context, the groups such as the acetals and thioacetalsmay be considered to be protected aldehydes. Iodinated aldehydes, suchas iodinated benzyl aldehyde, iodinated phenyl aldehyde or iodinatedphenoxyaldehyde, are particularly useful and they are widely availableand give good reaction yields.

Thus, preferably the radiopaque species is a compound of the formula IV:

wherein

A is a group capable of forming a cyclic acetal with a 1.2 diol or 1,3diol.

Preferably A is an aldehyde, acetal, hemiacetal, thioacetal ordithioacetal group;

Preferably A is —CHO, —CHOR¹OR² —CHOR¹OH, —CHSR¹OH or —CHSR¹SR² WhereinR¹ and R² are independently selected from C₁₋₄ alkyl, preferably methylor ethyl.

Specific examples of radiopaque species that have been shown to produceradiopaque PVA hydrogel microspheres include 2,3,5-triiodobenzaldehyde,2,3,4,6-tetraiodobenzyaldehyde and 2-(2,4,6-triiodophenoxy)acetaldehyde

In a further aspect the invention provides a radiopaque hydrogelmicrosphere obtained or obtainable by the reaction of a polymercomprising 1,2-diol or 1,3-diol groups with a halogenated aldehyde, ahalogenated acetal or a halogenated hemiacetal a halogenated thioacetalor a halogenated dithioacetal.

In a preferred embodiment of this aspect the radiopaque hydrogelmicrosphere is obtained by the reaction of an acrylamido polyvinylalcohol-co-acrylamido-2-methylpropane sulphonate hydrogel microspshere.These microspheres, examples of which are disclosed in U.S. Pat. No.6,676,971, U.S. Pat. No. 7,070,809 and WO 2004/071495, have been foundto react rapidly with iodinated aldehydes, iodinated acetals andiodinated thioacetals to yield radiopaque microspheres with high iodinecontent and provide good contrast in-vivo. The physical characteristics(size, shape, charge, drug loading ability etc) are not adverselyaffected by iodination and in some cases are improved. Handling alsoappears to be largely unaffected. Mechanical robustness is preserved andthe beads do not aggregate and suspend well in contrast agent and otherdelivery vehicles, such that delivery through a catheter may be achievedwith relative ease. Delivery has been observed to be smooth and even,without any blocking of the catheter. Furthermore, the beads are stableto steam and autoclave sterilization methods.

Particularly suitable iodinated aldehydes include, but are not limitedto, 2,3,5-triiodobenzaldehyde, 2,3,4,6-tetraiodobenzyaldehyde and2-(2,4,6-triiodophenoxy)acetaldehyde

The radiopaque microspheres and compositions described above may be usedin a method of treatment in which the microspheres described herein orcomposition comprising them is administered into a blood vessel of apatient to embolise said blood vessel. The blood vessel is likely oneassociated with solid tumour, such as hypervascular hepatic tumoursincluding hepatocellular carcinoma (HCC) and some other hepaticmetastases including metastatic colorectal carcinoma (mCRC) andneuroendocrine tumours (NETs). The methods of treatment are imageableand provide the clinician with good visual feedback on the procedure inreal-time or near real-time. Such methods are particularly useful wherea pharmaceutical active is loaded into the microspheres, and thetreatment provides for the delivery of a therapeutically effectiveamount of the active to a patient in need thereof.

The radiopaque microspheres may also be used in procedures in which themicrospheres are delivered to the site of action by injection. Oneapproach to this is the delivery of microspheres comprisingpharmaceutical actives directly to tumours by injection.

The present invention also provides compositions and microspheres of theinvention for use in the methods of treatment described above.

The microspheres described herein are surprisingly efficient in loadingand eluting drugs. The microspheres readily load positively chargeddrugs, such as i.a. doxorubicin, epirubicin, daunorubicin, idarubicinand irinotecan. Experimental studies have shown that the ability of themicrosphere to load and elute drug is the same before beads are renderedradiopaque using the chemistry of the invention as it is after reaction.In some cases, drug loading efficiency or capacity is surprisinglyimproved by more than 50%. In some cases, an increase of 100% in drugloading has been measured. In many cases, the extent of drug elution isunaffected, as compared to the non-radiopaque version of the beads, insome cases with substantially all of the drug eluted from the bead overa sustained period. In many cases the drug elution profile is improvedin that the time over which drug is eluted from radiopaque microspheresis increased as compared to equivalent non-radiopaque microspheres. Themicrospheres of the invention thus, surprisingly provide increased drugloading efficiency and improved i.e. prolonged drug-elution over theirnon-radiopaque equivalents.

The polymers or microspheres of any of the above aspects and embodimentsof the invention may be used in another aspect of the invention in whicha method of imaging an embolization procedure is provided. In a furtheraspect a method of monitoring embolization after the completion of aprocedure is provided. Depending on the permanent or rate ofbiodegradation of the radiopaque polymers of the invention, thepost-procedural window in which the embolization may be monitored can bein the range of days, weeks or even months.

The invention will now be described further by way of the following nonlimiting examples with reference to the figures. These are provided forthe purpose of illustration only and other examples falling within thescope of the claims will occur to those skilled in the art in the lightof these. All literature references cited herein are incorporated byreference.

FIGURES

FIG. 1 is micrograph of radiopaque hydrogel beads prepared according tothe examples. The beads shown are 75-300 μm, sieved after iodination,under different lighting conditions.

FIG. 2 is microCT image of radiopaque beads prepared according to theinvention. FIG. 2A is a 3D radiograph of radiopaque beads. FIG. 2B showsa 2D microCT image. The line profile (FIG. 2C) shows: the x-axis (μm) isthe length of the line drawn (shown in red across a section of theradiograph; and the y-axis indicates the level of intensity, using greyscale values, ranging from 0 (black) to 255 (white).

FIG. 3 shows light micrographs of sterilized radiopaque beads preparedaccording to the invention, before and after loading with doxorubicin.FIG. 3A shows the radiopaque beads prior to loading and FIG. 3B showsthe drug-loaded beads.

FIG. 4 shows the elution profile of RO and non RO beads loaded withdoxarubicin. The beads were 70-150 um in diameter. RO beads were 158 mgI/ml wet beads. Both bead types were loaded with 50 mg doxarubicin perml wet beads.

FIG. 5 shows the elution profile of RO beads loaded with sunitinib.

FIG. 6 shows the elution profile of RO and non RO beads loaded withsorafinib. RO beads were of size 70-150 um and had an iodine content 134mg I/ml wet beads.

FIG. 7 shows the elution profile of RO and non RO beads loaded withvandetanib. The beads were 70-150 um in diameter. RO beads were 158 mgI/ml wet beads.

FIG. 8 shows the elution profile of RO and non RO beads loaded withmiriplatin. Beads were of size 70-150 um and RO Beads had an iodinecontent 134 mg I/ml wet beads.

FIG. 9 shows the elution profile of RO and non RO beads loaded withtopotecan. RO and Non RO beads had a size of 70-150 um and RO beads hadan iodine level of 146 mg I/ml wet beads.

FIG. 10 shows sample cross section micro CT images of 10 RO beadsprepared according to the invention alongside water and air blanks.

FIG. 11 shows CT scans taken from a single swine following embolisationusing the RO beads of the invention.

(a) Pre embolisation; (b) 1 hr post embolisation; (c) 7 days postembolisation; (d) 14 days post embolisation. Arrows indicate RO beads inthe vessels.

Throughout these examples the structure of polymer comprising 1,2-diolor 1,3-diol groups is represented by the following structure:

EXAMPLES Example 1 Preparation of 2,3,5-triiodobenzaldehyde from2,3,5-triiodobenzyl alcohol

In a 50 ml three-necked round-bottomed flask fitted with a thermometer,a nitrogen bubbler and an air-tight seal, 10.2 g of the alcohol wasdissolved in 100 ml of anhydrous DMSO under a nitrogen blanket andstirring conditions. Then, 1.0 molar equivalent of propane phosphonicacid anhydride, (T3P), (50% solution in ethyl acetate) was added drop bydrop over 5 minutes at 22° C. to 25° C. The reaction solution wasstirred at room temperature and monitored by high performance liquidchromatography (Column: Phenominex Lunar 3 um C₁₈: Mobile Gradient:Phase A water 0.05% TFA, Phase B ACN 0.05% TFA, linear gradient A to Bover 10 mins: Column temp. 40° C.: flow rate 1 ml per min: UV detectionat 240 nm). The conversion finished after 240 minutes. The yellowsolution was poured into 100 ml of deionised water while stirring,yielding a white precipitate which was filtered, washed with the motherliquors and 50 ml of deionised water. The cake was slurried in 50 ml ofethyl acetate, filtered and washed with 50 ml of water again, dried subvacuo at 40° C. for 20 hours to yield 7.7 g of a white solid. Thestructure and purity were confirmed by NMR analysis and high performanceliquid chromatography.

Example 2 Preparation of 2-(2,3,5-triiodophenoxy)acetaldehyde

a) Synthesis of 2-(2,4,6-triiodophenoxy)ethanol from 2,4,6-triiodophenol

In a 500 ml three-necked flat-bottomed flask fitted with a thermometer,a nitrogen bubbler and an overhead stirrer, 10 g of phenol weredissolved in 100 ml of ethanol, under a nitrogen blanket and vigorousstirring conditions at room temperature. 1.25 molar equivalent of sodiumhydroxide pellets were added and the slurry was stirred under a nitrogenblanket for 30 minutes until complete dissolution of the pellets. Then,1.1 molar equivalents of 2-iodoethanol were added, maintaining thetemperature at 25° C. and stirring for 15 minutes. The solution washeated to reflux of ethanol. The consumption of the phenol and formationof 2-(2,4,6-triiodophenoxy)ethanol were monitored by HPLC (conditions asper Example 1). After 25 hours, an additional 0.27 molar equivalents of2-iodoethanol was added and the solution was stirred for a further 2hours at reflux. After cooling the solution to room temperature, 150 mlof deionised water were added quickly under vigorous stirringconditions. The resulting slurry was filtered under vacuum, washed withthe mother liquors, three times 30 ml of deionised water and finallywith 5 ml of ethanol. The resulting pink cake was taken up into 100 mlof ethyl acetate and the organic layer extracted with copious amounts ofa sodium hydroxide solution (pH 14), dried over magnesium sulphate andconcentrated on a rotary evaporator to yield 5.9 g of an off-pink solid,which was identified as 2-(2,4,6-triiodophenoxy)ethanol by comparativeanalysis with a commercial analytical standard from sigma-aldrich.

(b) Oxidation of 2-(2,4,6-triiodophenoxy)ethanol to2-(2,3,5-triiodophenoxy) acetaldehyde

In a 500 ml three-necked flat-bottomed flask fitted with a thermometer,a nitrogen bubbler and an overhead agitator, 5.9 g of the alcohol wasdissolved into 150 ml of anhydrous DMSO under a nitrogen blanket. Thesolution was stirred and heated to 40° C., and 1.6 molar equivalents ofT3P (50% w/w solution in EtOAc) were added slowly while maintaining thetemperature at 40° C. to 41° C. The consumption of alcohol andproduction of aldehyde was monitored by high performance liquidchromatography over time (conditions as per Example 1). After 24 hours,150 ml of water were added slowly to the reaction mixture over 2 hoursusing a syringe pump. An off-pink solid precipitated out of the solutionand was filtered under vacuum to yield a pink cake which was washed withwater. The resulting impure flocculate was taken up in ethyl acetate andhexane, then concentrated under vacuum at 40° C. to yield an oilidentified as 2-(2,3,5-triiodophenoxy)acetaldehyde by 1H NMR analysis.

Example 3 Preparation of1-(2,2-dimethoxyethoxymethyl)-2,3,5-triiodo-benzene from2,3,5-triiodobenzyl alcohol and 2-bromo-1,1-dimethoxy-ethane (Example ofa radiopaque acetal/protected aldehyde)

In a 50 ml three-necked flat-bottomed flask fitted with an overheadagitator, a thermometer, a nitrogen bubbler and a gas tight septum, 5.07g of the alcohol were dissolved in 55 ml of anhydrous2-methyltetrahydrofuran under a nitrogen blanket and stirringconditions. Then, 2.11 g of the acetal followed by 0.540 g of sodiumhydride (60% dispersion in mineral oil) were added. The slurry washeated to reflux under a nitrogen blanket for 1010 minutes and monitoredby high performance liquid chromatography (conditions as per Example 1).The reaction mixture was taken up into 50 ml of dichloromethane andwashed four times with 25 ml of water. The organic layer wasconcentrated sub vacuo to yield a brown oil, which was identified as1-(2,2-dimethoxyethoxymethyl)-2,3,5-triiodo-benzene by 1H NMR.

Example 4 Preparation of Cross-Linked Hydrogel Microspheres

Cross-linked hydrogel microspheres were prepared according to Example 1of WO 2004/071495. The process was terminated after the step in whichthe product was vacuum dried to remove residual solvents. Both High AMPSand low AMPS forms of the polymer were prepared and beads were sieved toprovide appropriate size ranges. Beads were either stored dry or inphysiological saline and autoclaved. Both High AMPS and low AMPS formsof the polymer can used with good radiopacity results

Example 5 General preparation of radiopaque microspheres from2,3,5-triiodobenzaldehyde and preformed cross-linked PVA hydrogelmicrospheres

In a 50 ml three-necked round-bottomed flask fitted with an overheadagitator, a thermometer and a nitrogen bubbler, 1.0 g of dry PVA-basedbeads (see Example 4—High AMPS version) were swollen in an appropriatesolvent (e.g. DMSO) under a nitrogen blanket and stirring conditions.Then, 0.20 to 1.5 molar equivalents of aldehyde (prepared according toexample 1) were added to the slurry, immediately followed by 1.0 to 10molar equivalents of acid (e.g. sulphuric acid, hydrochloric acid,methanesulfonic acid or trifluoroacetic acid—methanesulfonic acid istypically used). The theoretical level of available —OH groups wasestimated based on the characteristics of the PVA used and the degree ofcross linking (typical values for high AMPS beads=0.0125 mol/gm drybeads). The reaction slurry was stirred at 50° C. to 130° C. for between12 hours and 48 hours, while the consumption of aldehyde was monitoredby high performance liquid chromatography (HPLC). When required, adesiccant such as magnesium sulphate or sodium sulphate was added todrive the reaction further. In this way batches of radiopaquemicrospheres having differing levels of iodine incorporation could beobtained. When enough aldehyde had reacted on the 1,3-diol of thePVA-based hydrogel to render it sufficiently radiopaque (see below), thereaction slurry was cooled to room temperature and filtered. The cake ofbeads was washed with copious amount of DMSO and water, until free fromany unreacted aldehyde, as determined by high performance liquidchromatography.

Example 6 Preparation of radiopaque microspheres from 2,3,5-triiodobenz-aldehyde and a cross-linked PVA hydrogel microsphere

5.0 g of dry PVA-based beads (see Example 4—High AMPS version 105-150um) and 0.26 equivalents of aldehyde (7.27 g) (prepared according toExample 1) placed in a 500 ml vessel purged with nitrogen. 175 mlanhydrous DMSO were added under a nitrogen blanket and stirred to keepthe beads in suspension. The suspension was warmed to 50 C and 11 ml ofmethane sulphonic acid was added slowly. The reaction slurry was stirredat 50° C. for between 27 hours, while the consumption of aldehyde wasmonitored by HPLC. The reaction slurry was then washed with copiousamount of DMSO/1% NaCl followed by saline. The resultant beads had aniodine concentration of 141 mg I/ml wet beads and had a radiopacity of4908 HU.

Example 7 Preparation of Radiopaque PVA hydrogel beads with2-(2,4,6-triiodophenoxy)acetaldehyde

2-(2,4,6-triiodophenoxy)acetaldehyde was prepared according to Example 2and reacted with PVA-based hydrogel beads (see Example 4 high AMPSversion) following the same method as Example 5 but with the temperatureof the reaction maintained between 20° C. and 50° C. The reaction timewas also reduced to less than one hour. Iodine content was determined tobe 18 mg I/ml wet beads.

Example 8 Preparation of radiopaque PVA hydrogel microspheres with1-(2,2-dimethoxyethoxymethyl)-2,3,5-triiodo-benzene

In a 50 ml three-necked flat-bottomed flask fitted with an overheadagitator, a thermometer and a nitrogen bubbler, 1.0 g of dry PVA-basedbeads (see Example 4 high AMPS version) were swollen in an appropriatesolvent (e.g. DMSO) under a nitrogen blanket and stirring conditions.Then, 0.5 molar equivalents of aldehyde(1-(2,2-dimethoxyethoxymethyl)-2,3,5-triiodo-benzene, prepared accordingto Example 3) were added to the slurry, immediately followed by 163 μlof methanesulfonic acid. The reaction slurry was stirred at 40° C. for80 minutes, and then heated to 80° C. for 200 minutes, while theconsumption of aldehyde was monitored by high performance liquidchromatography. As enough aldehyde had reacted on the 1,3-diol of thePVA-based hydrogel to render it sufficiently radiopaque after this time,the reaction slurry was cooled to room temperature and filtered. Thecake of beads was washed with copious amounts of DMSO and water, untilfree from any unreacted acetal and aldehyde, as determined by highperformance liquid chromatography. Iodine content of the beads wasdetermined to be 31 mg/ml wet beads.

Example 9 Preparation of Radiopaque PVA hydrogel microspheres from2,3,4,6 tetraiodobenzaldehyde

2,3,4,6-tetraiodobenzyl alcohol (ACES Pharma; USA) was converted to2,3,4,6 tetraiodobenzaldehyde using T3P and DMSO as described inExample 1. 0.6 molar equivalents of 2,3,4,6 tetraiodobenzaldehyde (8.8g) was then added to 2.05 g of PVA hydrogel microspheres (see Example4—size 150-250 μm high AMPS version) with DMSO under a nitrogen blanket.The reaction mix was heated to 50° C. and stirred for several hours. Thereaction was monitored with HPLC and when complete, the beads werefiltered and washed with DMSO, water and then 0.9% saline. Theradiopaque beads were then stored in a solution of 0.9% saline foranalysis. Iodine content was determined to be 30 mg/ml wet beads.

Example 10 Characterization of Radiopaque Beads

A light micrograph of the beads, typical of those produced by Examples(5 and 6) is shown in FIG. 1. The dry weight of beads was measured byremoving the packing saline and wicking away remaining saline with atissue, the beads were then vacuum dried under 50° C. overnight toremove water, and the dry bead weight and solid content (w/w %) ofpolymer were obtained from this.The iodine content (w/w %) in dry, beads were measured by elementalanalysis according to the Schöniger Flask method. For iodine content inwet beads, the calculation is:

Bead solid content (%)×iodine content in dry beads (%)

The solid content of radiopaque hydrogel beads, prepared according toExample 5 in a 0.9% saline was measured to be between 5% and 16%, w/w,while the weight/weight dry iodine content was measured to be between 5%and 56%, depending on the chemistry and the reaction conditions used.

An alternative way to express the iodine content is mg I/mL wet beads(wet packed bead volume), which is the same as the unit used forcontrast media. Using protocols according to Example 5, iodine contentin the range 26 mg I/ml beads to 214 mg I/ml beads was achieved.

Using similar protocols, but microspheres based on a low AMPS polymer(Example 4), higher iodine contents (up to 250 mg I/ml beads) could beachieved.

Example 11 MicroCT Analysis of Radiopaque Beads

Micro-CT was used to evaluate the radiopacity of samples of radiopaqueembolic Beads prepared according to Example 5 above

The samples were prepared in Nunc cryotube vials (Sigma-Aldrich productcode V7634, 48 mm×12.5 mm). The beads were suspended in 0.5% agarose gel(prepared with Sigma-Aldrich product code A9539). The resultingsuspension is generally referred to as a “Bead Phantom”. To preparethese bead phantoms, a solution of agarose (1%) is first raised to atemperature of approximately 50° C. A known concentration of the beadsis then added, and the two gently mixed together until the solutionstarts to solidify or gel. As the solution cools it gels and the beadsremain evenly dispersed and suspended within the agarose gel.

Bead phantoms were tested for radiopacity using micro-ComputerTomography (μCT) using a Bruker Skyscan 1172 μCT scanner at the RSSLLaboratories, Reading, Berkshire, UK, fitted with a tungsten anode. Eachphantom was analysed using the same instrument configuration with atungsten anode operating at a voltage of 64 kv and a current of 155 IA.An aluminium filter (500 μm) was used.

Acquisition Parameters:

Software: SkyScan 1172 Version 1.5 (build 14)

-   -   NRecon version 1.6.9.6    -   CT Analyser version 1.13.1.1

Source Type: 10 Mp Hamamatsu 100/250

Camera Resolution (pixel): 4000×2096

Camera Binning: 1×1 Source Voltage kV: 65 Source Current uA: 153 ImagePixel Size (um): 3.96 Filter: Al 0.5 mm

Rotation Step (deg): 0.280

Output Format: 8 bit BMP Dynamic Range: 0.000-0.140 Smoothing: 0 BeamHardening: 0

Post Alignment: corrected

Ring Artefacts: 16

A small amount of purified MilliQ water was carefully decanted into eachsample tube. Each sample was then analysed by X-Ray micro-computertomography using a single scan, to include the water reference and thebeads. The samples were then reconstructed using NRecon and calibratedagainst a volume of interest (VOI) of the purified water reference. Aregion of interest (ROI) of air and water was analysed after calibrationto verify the Hounsfield calibration.

Radiopacity was reported in both greyscale units and Hounsfield unitsfrom line scan projections across the bead. Values used for dynamicrange for all samples in NRecon (thresholding): −0.005, 0.13 (minimumand maximum attenuation coefficient). A typical image and line scan isshown in FIG. 2.

Table 1 gives the radiopacity of microspheres prepared according toExample 4 under varying conditions of time and equivalents of aldehyde,in both greyscale and Hounsfield units. Radiopacity data are the mean often line scans of beads of approximately 150 microns.

TABLE 1 Iodine (mg Mean bead I/ml) Grey scale HU size (um) 158 79 5639158 147 69 4626 146 141 74 4799 131 130 56 3600 153

FIG. 10 shows a sample of cross section images of 10 beads with anaverage size of 153 um, and average radiopacity of 4908 HU.

Example 12 Drug Loading of Radiopaque Beads Example 12(a) Doxorubicin

1 mL of RO bead slurry prepared according to Example 5 (size 100-300 um,iodine 47 mg I/ml wet beads) was measured by using a measuring cylinder,and the liquid removed. 4 mL of doxorubicin solution (25 mg/mL) wasmixed with the radiopaque beads with constant shaking at ambienttemperature. After 20 hr loading, the depleted solution was removed, andthe drug-loaded beads were rinsed with deionised water (10 mL) 4-5times. By measuring the doxorubicin concentration of combined depletedloading solution and rinsing solutions at 483 nm on a Varian UVspectrophotometer, the doxorubicin loaded was calculated as 80 mg/mLbeads. The doxorubicin hydrochloride drug loading capacity of theradiopaque beads was determined to be a non-linear function of theiodine content in the beads.

In a separate experiment 1.5 ml of RO beads of 70-150 um having aniodine content of 158 mg/ml wet beads were loaded as above using 3 ml ofdoxorubicin solution (25 mg/ml). Control, non RO beads of the same size,were also loaded in the same manner. The RO beads loaded 50 mgs/ml ofdoxorubicin whilst the control beads loaded 37.5 mgs/ml.

In a separate experiment, loading of RO beads (size 70-150 um; iodinecontent 150 mg I/ml), was essentially complete after 3 hrs.

Radiopaque beads prepared according to Example 5 above were loaded with37.5 mg/ml of Doxorubicin solution as per the above method. FIG. 3Ashows the radiopaque beads prior to loading and FIG. 3B shows thedrug-loaded beads. Prior to drug loading the beads were observed asspherical microspheres with a pale to dark brown tinge. When thedoxorubicin was loaded into the beads they turned a strong red colour.In this example, the beads were autoclaved to demonstrate to stabilityof the beads during sterilization. Bead integrity was preserved duringautoclaving; the mean bead size during autoclaving reduced from 177 μmto 130 μm. Further shifts in the bead size distribution were observedwhen beads were loaded with Doxorubicin, which is consistent withdrug-loading observed with non-radiopaque beads. In a further example,the mean bead size reduced on drug loading at 51 mg/ml, from 130 μm to102 μm. The resulting beads remain within the range that is clinicallyuseful, even after modification, sterilization, and drug-loading.

Example 12(b) Epirubicin

Epirubicin was loaded into RO beads (made according to Example 5) andnon RO beads (size, 70-150 um high AMPS made according to Example 4) inthe same manner as for doxorubicin. 1 ml of beads was loaded using a 1.5ml loading solution (25 mg/ml epirubicin). The final loading in theradiopaque beads was 37.49 mg (99.97% loading efficiency) and for thenon RO beads 36.43 (97.43% loading efficiency) after 90 mins.

Example 12(c) Sunitinib

Sunitinib DMSO solution was prepared by dissolving 400 mg of sunitinibpowder in anhydrous DMSO in a 10 mL volumetric flask. 1 ml of RO beadslurry (70-150 um, 134.4 mg I/ml wet beads prepared according to Example5). was prewashed with 10 ml of DMSO three times to remove waterresidue. 2.5 mL of the sunitinib-DMSO solution (40 mg/mL) was mixed withthe RO bead slurry and allowed to mix for 1-2 hr. Subsequently, afterremoving the loading solution, 10 mL of saline was added to the beadslurry to allow sunitinib to precipitate inside the beads. The washsolution and drug particles were filtered through a cell strainer, andthe washing was repeated three to four times. Non RO beads (100-300 um,prepared according to Example 4) were treated in the same manner.

Example 12(d) Sorafinib

1 ml of RO PVA microspheres (size 70 to 150 um, iodine content 134 mgiodine/ml beads, prepared according to Example 5) or non RO PVAmicrospheres (DC Bead™ 100-300. Biocompatibles; UK) were prewashed with10 ml of DMSO three times to remove water residue. Sorafenib/DMSOsolution (39.8 mg/mL in anhydrous DMSO) was mixed with 1 mL of beadslurry for 1 hr, (2.5 mL for the radiopaque bead and 2 mL for the nonradiopaque bead). After removing the loading solution, 20 mL of salinewas added to the bead slurry. The bead suspension was filtered through acell strainer, and the wash was repeated three or four times. The finalloading level was determined by DMSO extraction of small fraction ofhydrated beads and determination of drug concentration by HPLC (Column:Kinetex 2.6u XB-C18 100 A 75×4.60 mm; mobile phasewater:acetonitrile:methanol:trifluoroacetic acid 290:340:370:2 (v/v);detection 254 nm; column temperature 40° C.; flow rate: 1 mL/min).

49.9 mg of sorafinib was loaded into 1 ml RO beads and 34.7 mg wasloaded into 1 ml of non-RO (DC Bead™) beads.

Example 12(e) Vandetinib

A solution of 20 mg/ml vandetanib was prepared by dissolving 500 mg ofvandetanib in 14 ml of 0.1M HCl in a 25 ml amber volumetric flask withsonication, and making up to 25 ml with deionised water. Vandetanib wasthen loaded into both RO PVA hydrogel microspheres (prepared accordingto Example 5: Size 70 to 150 um; Iodine content 147 mg/ml beads) andnon-RO microspheres (DC Bead 100-300; Biocompatibles UK Ltd) accordingto the following protocol:

One millilitre of microspheres including packing solution was aliquotedby measuring cylinder and transferred into a 10 mL vial. The packingsolution was then removed using a pipette. Three millilitres of the 20mg/ml drug solution was then added to the non RO bead or 1.5 mL of thesolution to RO beads. In the radiopaque bead loading experiment the pHof the solution was between 4.6 and 4.8; in the DC bead loadingexperiment the pH was at approximately 4.2. After 2 hr. loading, theresidual solution was removed, and the beads were washed with 5 mL ofdeionised water 3 times. The depleted loading and washing solutions werecombined and analysed by C₁₈ reverse phase HPLC with detection at 254 nmto determine the loading yield. For sterilisation if, needed, the loadedbeads, in 1 ml of deionised water, were either autoclaved at 121° C. for30 min, or lyophilised for 24 hr and then gamma sterilised at 25 kGy.

Radiopaque beads loaded vandetanib to a level of 29.98 mg/ml of wetbeads.

Non radiopaque beads loaded vandetanib to a level of 26.4 mg/ml.

Example 12(f) Miriplatin

Hydrated RO microspheres (size 70-150 um, iodine content 134 mgiodine/ml beads, prepared according to Example 5) and non RO PVAmicrospheres (DC Bead 100-300, Biocompatibles; UK), 1 mL each vial, werewashed with 5 mL of 1-methyl-2-pyrrolidinone four times. The solvent wasthen removed. 0.147 g of miriplatin was mixed with 25 mL of1-methyl-2-pyrrolidinone, and the suspension was heated to 75° C. in awater bath to dissolve miriplatin. 2 mL of the drug solution was addedinto the washed beads and the mixture placed in a 75° C. water bath for1 hr. The bead suspensions were filtered through a cell strainer toremove the loading solution, followed by washing with about 100 mL ofsaline.

A known volume of beads was washed with deionised water and freezedried. Total platinum was determined by elemental analysis using ICP-OES(Inductively Coupled Plasma—Optical Emission Spectroscopy) and convertedto miriplatin level.

The experiment was repeated loading lyphilised beads in the same manner.Table 2 shows the results of loading miriplatin into wet and lyophilisedRO beads.

TABLE 2 Miriplatin loading data. Miriplatin content Miriplatin in wetbeads Bead sample (%) (μg) Non RO bead (wet loaded) 0.39 2058 RO Bead(wet loaded) 0.31 2645 RO bead (dry loaded) 0.12 1160

Example 12(g) Irinotecan

A 2 mL bead sample of Non RO beads (100-300 um—made according to Example4 high AMPS version) and RO Bead (100-300 um, 163 mg I/mL made accordingto Example 5) were mixed with 10 ml irinotecan solution in water (10mg/mL). Loading was measured by determining the irinotecan level indepleted loading solution by UV spectroscopy, at 384 nm. Both non RO andRO beads loaded approximately 100% of the drug within 90 min.

Example 12(h) Topotecan

A 1 mL bead sample of Non RO beads (70-150 um—made according to Example4 high AMPS version) and RO Bead (70-150 um, 146 mg I/mL made accordingto Example 5) were mixed with topotecan solution in water (15.08 mg/mL)to load dose of 40 mg (2.5 ml) or 80 mg (5 ml) under agitation. Afterabout 1.5 hr, the loading of topotecan was measured by determining thetopotecan level in depleted loading solution as described above, by UVspectroscopy, at 384 nm. Table 3 shows maximum of 80 mg topotecan wasloaded in RO bead sample. Both non RO and RO beads loaded >98% of 40 mgtopotecan.

TABLE 3 Topotecan loading in RO and non RO beads Time (hrs) Drug loaded(mg) % Drug Loaded RO bead, 1 mL 1.5 40 100 RO bead, 1 mL 1.5 80 100 NonRO bead, 1 mL 1.5 39 98

Example 13 Drug Elution from Radiopaque Beads Example 13(a) Doxorubicin

Doxorubicin-loaded beads prepared in the according to Example 13(a)(70-150 um, 158 mg I/ml, 50 mg/ml doxorubicin) were added to 1000 ml ofPBS, in a brown jar at room temperature. The bead suspension was stirredwith a magnetic stirrer at low speed. At sampling time points, 1 mL ofelution media were removed through a 5 um filter needle and analysed byUV at 483 nm against a standard. The elution profiles were shown in FIG.4.

Example 13(b) Sunitinib

Sunitinib-loaded beads prepared according to Example 13(c) were added to400 ml of PBS, 0.5 g/L Tween 80 in a brown jar at 37° C. in a waterbath. The bead suspension was stirred with a magnetic stirrer at lowspeed. At sampling time points of 1, 2, 3 and 4 hours, 10 mL of elutionmedia were removed through a 5 um filter needle for HPLC analysis(conditions as per Example 13(c)) and 10 mL of fresh PBS solution wasadded to make up the volume. At sampling time-points of 5, 25, 48 and 73hours, 100 mL of elution media were replaced with equal volume of freshPBS solution. The sample was analysed by HPLC. The elution profile isillustrated in were shown in FIG. 6.

Example 13(c) Sorafinib

Sorafenib-loaded beads prepared according to Example 13(d) were added to400 mL of PBS with 0.5 g/L Tween 80 in a brown jar in a 37° C. waterbath. The bead suspension was stirred with a magnetic stirrer at lowspeed. At sampling time points of 1, 2, 4, and 6 hours, 10 mL of elutionmedia were removed through a 5 um filter needle for HPLC analysis and 10mL of fresh PBS solution was added to make up 400 mL volume. At samplingtime-points 8, 24.5 and 31 hrs, 100 mL of elution media were replacedwith equal volume of fresh PBS solution. Two replicates were run foreach type of beads. The elution profiles of sorafenib from RO beads andnon RO beads are shown in FIG. 6.

Example 13 (d) Vandetinib

Vandetinib loaded RO and non RO beads prepared according to Example13(e) (2 ml beads at 30 mg vandetinib/ml beads, beads 70-150 um and RObeads having 141 mg I/ml wet beads) were placed in Amber jars containing500 mL of PBS with magnetic flea, at ambient temperature. At eachsampling time-point, the complete PBS elution medium was removed fromthe jar through a cannula filter by a peristaltic pump, and replacedwith the same volume of fresh PBS. 5 ul of the elution medium wasanalysed by C₁₈ reverse phase HPLC with detection at 254 nm. The elutionprofile is illustrated in FIG. 7

Example 13(e) Miriplatin

Miriplatin-loaded beads made according to Example 13(f) were added to 50mL of PBS with 1% of Tween 80 in 100 mL Duran® bottles. The bottles weresuspended in a 37° C. water bath and rotated at 75 rpm to agitate thebeads. At sampling time points of 1, 5, 11, 15 and 22 days, 20 mL ofelution medium was removed for ICP analysis and 20 mL of fresh PBS/Tweensolution was added to make up 50 mL volume. The elution profiles ofmiriplatin from RO beads and non RO beads are shown in FIG. 8.

Example 13(f) Irinotecan

A sample of beads prepared in example 13(g) 163 m I/ml were added to 500ml of PBS, in a brown jar at 37° C. and stirred with a magnetic stirrerat low speed. At sampling time points, 1 ml of elution media wereremoved through a 5 um filter needle and analysed by UV at 369 nmagainst a standard. The elution profiles were shown in FIG. 9.

Example 14 Radiopacity of Drug-Loaded Radiopaque Beads

An aliquot of the doxorubicin loaded beads prepared according to Example13 were subjected to microCT analysis in the same way as described inexample 12. The drug-loaded beads were found to be radiopaque. Theaverage Bead Radio-opacity (Grey Scale) was determined to be 139 (n=3).

Example 15 Freeze Drying Protocol

Microspheres of the invention, whether drug loaded or non-drug loaded,may be freeze dried according to the protocol described in WO07/147902(page 15) using an Epsilon 1-6D freeze dryer (Martin ChristGefriertrocknungsaniagen GmbH, Osterode am Harz, Germany) with LyoScreen Control (LSC) panel and Pfeiffer DUO 10 Rotary Vane Vacuum pumpand controlled by Lyolog LL-1 documentation software, as brieflydescribed below.

The microspheres are lyophilised by freezing at about −30° C. without avacuum, for at least 1 h, then reducing the pressure gradually over aperiod of about half an hour to a pressure of in the range 0.35-0.40mbar, while allowing the temperature to rise to about −20° C. Thetemperature and pressure conditions are held overnight, followed byraising the temperature to room temperature for a period of about 1-2hours at the same time pressure, followed by a period at roomtemperature with the pressure reduced to about 0.05 mbar, to a totalcycle time of 24 hours.

If preparations are required to be maintained under reduced pressure, atthe end of the cycle and substantially without allowing ingress of airthe vials are stoppered under vacuum by turning the vial closingmechanism that lowers the shelves to stopper the vials on the shelfbeneath. The chamber is then aerated to allow the chamber to reachatmospheric pressure. The shelves are then returned to their originalposition and the chamber opened. If the samples are not maintained underreduced pressure, then the pressure is gradually returned to atmosphericbefore stoppering.

Example 16 In Vivo Embolisation Study

Male domestic Yorkshire crossbred swine (approximately 14 weeks old)were used in the study.

After induction of anesthesia, a sheath was placed in the femoral arteryand, under fluoroscopic guidance, a guide wire was passed through theintroducer and moved through to the aorta. A guide catheter, passed overthe guide wire, was then placed at the entrance to the coeliac artery.The guide wire was removed, and contrast medium used to visualize thebranches of the coeliac artery.

A micro-wire/micro-catheter combination was passed through the guidecatheter and used to select the common hepatic artery, isolating 25 to50% of the liver volume. A micro-catheter was passed over the guide wireinto the liver lobe, the guide wire was removed and contrast medium usedto capture an angiogram of the lobe. Digital subtraction angiography wasperformed to confirm the catheter position.

2 mls of RO beads, prepared according to Example 5 (size 75-150 um,iodine content 141 mg I/ml) was transferred to a 20 to 30 mL syringe andthe packing solution discarded. A smaller syringe holding 5 mL ofnon-ionic contrast medium (Visipaque® 320) was connected to the largersyringe via a three-way stopcock and the beads mixed with the contrastby passage through the stopcock. The total volume was adjusted to 20 mLby addition of contrast. This suspension was administered slowly underfluoroscopic guidance, until near stasis was achieved. The volume ofsuspension delivered to achieve stasis was between 2 and 6 mls.

Abdominal CT images were taken pre-dose, 1 and 24 hours post dose, andon Days 7 and 14. On Day 14, a baseline CT image was taken and 75 cc ofcontrast material was injected. Post-contrast material injection, asecond CT image was taken. The images were analyzed for the extent ofvisibility of beads in the liver.

The RO beads were visible on X-ray during the procedure and on CT. Thiswas best shown on the 7 and 14 day CT scans, obtained without IVcontrast (see FIG. 11). The beads were easily visible in multiplebranches of the hepatic arteries. The beads were more attenuating than,and can be differentiated from, IV contrast.

1. A hydrogel comprising 1,2-diol or 1,3-diol groups acetalised with aradiopaque species the radiopaque species comprising one or morecovalently bound radiopaque halogens.
 2. A hydrogel according to claim 1comprising 1,2-diol or 1,3-diol groups acetalised with a radiopaquespecies such that that the polymer comprises an iodinated aromatic groupcovalently bound to the polymer through cyclic acetal linkage.
 3. Ahydrogel according to claim 1, wherein the hydrogel is a cross-linkedpolymer network.
 4. A hydrogel according to claim 1 wherein the hydrogelcomprises polyvinyl alcohol (PVA) in which the PVA comprises pendentactetate groups formed from the acetalisation of PVA withN-acryloyl-aminoacetaldehyde dimethylacetal and which is cross-linkedwith 2-acrylamido-2-methylpropanesulfonic acid (PVA-AMPS).
 5. A hydrogelaccording to claim 1 wherein the radiopaque species is acetalised in thehydrogel in the form of a cyclic acetal.
 6. A hydrogel according toclaim 1 wherein the radiopaque species is selected from iodine andbromine.
 7. A hydrogel according to claim 6 wherein the radiopaquespecies comprises an iodinated or brominated phenyl group.
 8. A hydrogelaccording to claim 1 wherein the hydrogel comprises greater than 10%iodine by dry weight.
 9. A hydrogel according to claim 1 wherein thehydrogel is in the form of microparticles or microspheres.
 10. Ahydrogel according to claim 9 wherein the hydrogel is in the form ofmicrospheres with a mean diameter size range of from 10 to 2000 μm. 11.A hydrogel according to claim 1 in the form of microspheres ormicroparticles having a mean radiopacity of 500 HU or greater.
 12. Ahydrogel according to claim 1 wherein the hydrogel has a net charge atphysiological pH.
 13. A hydrogel according to claim 1 comprising astructure of the general formula I or II

wherein X is a group substituted by one or more halogens and preferablyone or more iodine moieties and J is a group of the formula —CH2- or isa bond.
 14. A hydrogel according to claim 13 wherein X is a group of theformula

wherein Z is a linking group, or is absent, such that the phenyl groupis bonded to the cyclic acetal; if Z is present, then Z is C1-6alkylene, C1-6 alkoxylene or C1-6 alkoxyalkylene; Hal is 1, 2, 3 or 4covalently attached radiopaque halogens.
 15. A composition comprising ahydrogel according to claim 1 and a therapeutic agent wherein thetherapeutic agent is absorbed into the hydrogel matrix.
 16. Acomposition according to claim 15 wherein the therapeutic agent iselectrostatically held in the hydrogel and elutes from the hydrogel inelectrolytic media.
 17. A method of making a radiopaque polymercomprising reacting a polymer comprising 1,2-diol or 1,3-diol groupswith a radiopaque species capable of forming a cyclic acetal with said1,2-diol or 1,3 diols under acidic conditions.
 18. A method according toclaim 17 wherein the polymer is cross-linked.
 19. A method according toclaim 17 wherein the polymer comprises polyvinyl alcohol (PVA) orcopolymers of PVA.
 20. A method according to claim 17 wherein theradiopaque species is an organic molecule or organometallic complex,which provides a radiopacity >1 HU, and which comprises a reactivemoiety selected from the group consisting of aldehydes, acetals,hemiacetals thioacetals and dithioacetals.
 21. A method according toclaim 17 in which the radiopaque species comprises iodine or bromine 22.A method according to claim 21 wherein the radiopaque species is aniodinated aldehyde.
 23. A method according to claim 22 wherein theradiopaque species is an iodinated benzyl aldehyde, iodinated phenylaldehyde or an iodinated phenoxyaldehyde.
 24. A method of making aradiopaque hydrogel microsphere comprising the steps of: (a) swelling apre-formed hydrogel microsphere comprising a polymer with 1,2-diol or1,3-diol groups in a solvent capable of swelling said microsphere; and(b) mixing the swollen beads with a solution of a radiopaque speciescapable of forming a cyclic acetal with said 1,2 or 1,3 diols underacidic conditions; and (c) extracting the microspheres.
 25. A methodaccording to claim 24 which further comprises the step of drying theextracted microspheres.
 26. A method according to claim 24 in which thereaction is conducted in polar organic solvent and at elevatedtemperature.
 27. A method according to claim 24 in which the radiopaquespecies comprises a functional group selected from the group consistingof aldehydes, acetals, hemiacetals, thioacetals and dithioacetals.
 28. Amethod according to claim 24 in which the radiopaque species comprisesiodine.
 29. A method according to claim 28 wherein the radiopaquespecies is an iodinated aldehyde.
 30. A method according to claim 28wherein the radiopaque species is an iodinated benzyl aldehyde, aniodinated phenyl aldehyde or an iodinated phenoxyaldehyde.
 31. A methodaccording to claim 30 wherein the radiopaque species is2,3,5-triiodobenzaldehyde, 2,3,4,6-tetraiodobenzyaldehyde or2-(2,4,6-triiodophenoxy)acetaldehyde.
 32. A method according to claim 24in which the preformed hydrogel microsphere comprises PVA with pendentactetate groups formed from the acetalisation of PVA withN-acryloyl-aminoacetaldehyde dimethylacetal and which is cross-linkedwith 2-acrylamido-2-methylpropanesulfonic acid.
 33. A method oftreatment in which a hydrogel according to claim 1 is administered intoa blood vessel of a patient to embolise said blood vessel.
 34. A methodaccording to claim 33 in which the blood vessel is associated with solidtumour.
 35. A method according to claim 33 in which the tumour ishepatocellular carcinoma.
 36. A hydrogel according to claim 1 for use inembolization of a blood vessel.
 37. A composition according to claim 1for use in embolization of a blood vessel.